Self-optimizing detergent controller for minimizing detergent set-point overshoot

ABSTRACT

An apparatus and method for programming a detergent controller to vary the detergent concentration set-point according to the time of day and to achieve detergent concentration levels quickly without incurring overshoot. Thus, the present invention insures that the warewashing machine is operated at optimum efficiency and cost. To vary the set-point according to the time of day, the invention combines the features of a microprocessor, a clock and a controller into one unit. The user enters the time setting and set point into the controller. The microprocessor then compares the real-time clock signal with the user time settings and outputs an appropriate set-point value from the microprocessor to the controller. To achieve detergent concentration levels quickly without incurring overshoot, the controller senses the detergent concentration and dispenses the proper detergent level to the warewashing machine according to a predetermined detergent feed time based on the previous response time and the programmed set-point. Thus, the controller can change the response function if and when conditions change.

This is a divisional of application Ser. No. 07/849,750, filed Mar. 12,1992, U.S. Pat. No. 5,404,893 which application is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates primarily to a method and apparatus forcontrolling the automatic addition of detergent into a commercialwarewashing machine. There are two key problems addressed by theinvention. One is the detergent addition itself. The other is thedetermination of an appropriate concentration set-point. By making thedetergent feed dependent upon the real-time concentration change rate,detergent overuse is reduced during the detergent addition. Adjustingdetergent concentration set-points to correspond to changing accountconditions also helps to maximize the performance of the warewashingprocess.

2. Description of Related Art

It is known in the art to provide warewashing machine systems withdetergent controllers. Typically, such systems operate in an on-offmode, proportional mode or a combination thereof. The systems controlthe detergent concentration level to a pre-set detergent concentrationlevel (set-point). The systems do not compensate for varying chemicalinjection rates and therefore exceed this set-point. They indirectlysense detergent concentration by measuring solution conductivity. Themajor perceived benefits of this type of controller is that the additionof, and concentration maintenance of, detergent to the warewashingmachine is achieved without manual intervention.

However, these controllers do have some major shortcomings. Thedetergent concentration set-point consists of a single pre-set value forall wash cycles. Unless the set-point is manually reset, the wash itemsare subjected to the same concentrations of detergent in the washsolution, regardless of the meal period or type of soil present on thewash items. Therefore, to be certain of maintaining an acceptablecleaning result, the set-point is selected for a worst case condition.This results in detergent overuse. In addition, the detergentcontrollers feed detergent based on proportional control, reacting tothe relationship between the setpoint and the current concentration.They do not compensate for the detergent feed rate which also causesdetergent overuse or excessive wear on the feeder equipment.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa programmable detergent controller for varying the detergentconcentration set-point according to the date and time. The controllersensor, a conductivity sensor with an imbedded thermistor, is capable ofnot only detecting detergent concentration and wash temperature but alsowater changeovers, machine run time, and detergent consumption. Thepresent invention also discloses a programmable detergent controller foroptimizing detergent concentration without incurring overshoot. Thus,the present invention insures that the warewashing machine is operatedat optimum efficiency and cost.

The present invention combines the features of a microprocessor, clockand controller into one unit. The present invention provides acontroller with the ability to change detergent concentration set-pointsaccording to the time of the day. The present invention also provides adetergent controller with the ability to reach a detergent concentrationlevel quickly without incurring overshoot.

A feature of the present invention is a controller which may beprogrammed with a variable detergent concentration set-point. A furtherfeature of the present invention is a controller which senses thedetergent concentration and dispenses the proper detergent amount to thewarewashing machine. An advantage of the present invention is theability to change the detergent concentration set-point to correspond tothe meal period or other special needs. Another advantage of the presentinvention is the ability to calculate the appropriate detergent feedtime based on the rate of detergent concentration change.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a diagram showing the interconnection between the warewashingmachine and the monitoring system;

FIG. 2 is a block diagram of the variable detergent concentrationset-point system incorporating a microprocessor, a clock and a detergenton-time controller; and

FIG. 3 is a flow chart diagram describing how the controller calculatesthe appropriate detergent feed time based upon the previous response anda programmed on-off set-point.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

The preferred embodiment of the present invention provides a system tocontrol detergent concentration set-points for warewashing machines withrespect to time. The present invention leverages the sensing capabilityof the detergent controller by adding a microprocessor and a clock intothe controller unit. By programming different detergent concentrationset-points for different times of the day, the variable detergentconcentration controller can more effectively remove soil from the washitems.

The preferred embodiment of the present invention also provides a systemto control the detergent concentration level without overshooting apre-set detergent concentration level. Detergent injection rates varywith temperature, concentration and other factors. The latency time thatresults from the feeder equipment injection delays and productdissolution rates is not accounted for in previous detergentcontrollers. The present invention compensates for any latency timewithout exceeding the detergent concentration set-point. Those skilledin the art will recognize that the present invention could be used withany type of warewashing machine.

FIG. 1 discloses the preferred embodiment of the present invention asused in a typical warewashing system. The preferred embodiment includesa detergent controller 12 that incorporates a microprocessor 10 and aclock 20 within a housing unit 8. The controller 12 also includes asolenoid valve 6 within the housing unit 8 to control the detergent feedto the warewashing system.

FIG. 2 more particularly illustrates the block diagram of the preferredembodiment as used in a variable detergent concentration set-pointsystem. The preferred embodiment includes a microprocessor 10 fordetermining an appropriate detergent concentration set-point. Themicroprocessor 10 receives two types of inputs from the user. First, aparticular detergent concentration set-point 14 is entered into themicroprocessor 10. Then, a user time setting 16 is entered into themicroprocessor 10. The user time setting 16 instructs the microprocessor10 to begin using the corresponding detergent concentration set-point atthe time entered.

Next, the preferred embodiment includes a clock device 20 that providesthe microprocessor 10 with a signal corresponding to the date and time22. The microprocessor 10 compares the date and time signal 22 to theuser time setting 16. When the clock date and time signal 22 coincideswith the user time setting 16, the microprocessor 10 loads thecorresponding detergent concentration set-point 14. The detergentcontroller 12 uses this corresponding detergent concentration set-point14 until the microprocessor 10 determines that another set-point shouldbe used. Thus, the controller 12 can be programmed to handle soil loadsthat vary cyclically with time. The number of time and set-point entriesare limited only by the storage capability of the microprocessor.

A sensor 24 routes a measurement of the detergent concentration andtemperature information 28 to the microprocessor 10. The sensor 24preferably comprises a conductivity sensor and an imbedded thermistor.The conductivity sensor signals the detergent concentration 28 bydetermining conductivity using the measurement of the free ions in thewash tank 40 solution. The imbedded thermistor signals the temperatureinformation 28 by determining the temperature of the wash tank 40solution.

In the preferred embodiment, the conductivity sensor may be of anelectrode or electrode-less type. An electrode-type conductivity sensoris typically comprised of two electrodes immersed in the wash tank 40solution, wherein the current flow from one electrode to the otherelectrode corresponds to the conductivity of the solution. Anelectrode-less conductivity sensor, which operates as a transformer, istypically comprised of a primary coil inducing a current into the washtank 40 solution and a secondary coil converting the current into avoltage level, wherein the voltage level corresponds to the conductivityof the solution.

The microprocessor 10 uses the conductivity and temperature information28 provided by the sensor 24 to determine wash tank 40 changeover,detergent consumption, and detergent feed.

With regard to wash tank 40 changeover, the microprocessor 10 candetermine when the wash tank 40 has been recharged with fresh waterusing the detergent concentration 28. Typically, the same solution isused over and over for multiple racks of dishes. The sensor 24 sensesthe fresh water because of the resulting change of the solution to avery low conductivity or a major reduction in conductivity.

With regard to detergent consumption, the detergent concentration 28from the sensor 24 can also be used to determine when a detergentreservoir is empty. If the sensor 24 detects a decrease in conductivity,even though the warewashing machine has been instructed to feeddetergent into the wash tank 40, then there is probably no detergentbeing fed into the wash tank 40. However, it could be the situation thatsomeone just recharged the detergent reservoir, but some air has gotteninto the feed line; it is also possible some of the detergent wassolidified and it is just eroding slowly in the wash tank 40 solution;or it is possible that there are other causes of low conductivity. Thus,the microprocessor 10 can be programmed not to indicate an emptydetergent reservoir unless the wash tank 40 solution remains at a lowconductivity level for some period of time. Other criteria can also beused.

With regard to detergent feed, the microprocessor 10 compares thecorresponding detergent concentration set-point 14 with the detergentconcentration 28 from the sensor 24. Based on this comparison, themicroprocessor 10 determines when the solenoid valve 6 should be openedto allow the feeding of detergent solution 30 into the wash tank 40 andsends a open command 26 to the solenoid valve 6.

FIG. 3 is a flow chart describing the steps performed by the controller12 (shown in FIGS. 1 and 2) during detergent feed to achieve yet, notexceed, a pre-set detergent concentration level. There must be a balancebetween overshoot and the need to reach a suitable detergentconcentration quickly to insure adequate washing performance on thefirst items through the process.

Instead of fixed or adjustable crossover points to proportional mode oradjustments to output response protocols, the controller 12 dispensesdetergent only by calculating the required feeder on-time, based on thelast known flow-rate. After, or in some cases during a detergent feedcycle, the detergent flow-rate is calculated and either the detergentfeed time is modified for the current detergent feed cycle or it will beused for the next detergent feed time calculation. This allows thecontroller to avoid any on-off type proportioning, and instead usederivative control to achieve the detergent concentration set-pointquickly and with minimal overshoot. It also inherently gives thecontroller 12 the capability to optimize detergent feed for any of avariety of configurations and system lags without the need to predictthem in advance. This learning and comparing cycle is performed eachtime the controller 12 activates a solenoid valve 6, thus allowing achange to the controller 12 response function if and when conditionschange, such as water pressure or temperature. The special challenges inthe warewashing application require the controller 12 to make up widedifferences between the actual detergent concentration 28 provided bythe sensor 24 and set-point as quickly as possible, again withoutexceeding set-point. Aggravating the process is a latency time betweenactivating the deteregent feed and reading the detergent concetrationinformation 28 at the wash tank sensor 24. The detergent feed rate canvary greatly and must be compensated for.

The controller 12 first reads an interrupt condition 50, FLAG 3. FLAG 3is an indication for the controller 12 to activate the solenoid valve 6to allow the feeding of detergent solution 30 into the wash tank 40. IfFLAG 3 has not been set, then the controller 12 is in the "control"state and the intermediate flow-rate calculation 60 begins immediately.If FLAG 3 has been set, then the controller 12 determines whether thesolenoid valve 6 will be activated for longer than 2 seconds 52, giventhe last known flow-rate (FC), the current detergent concentration (DC)and set-point (DS). If the detergent feed will not be ON longer than 2seconds, then the controller 12 does nothing 54. If the controller 12determines that the solenoid valve 6 will be activated for longer than 2seconds, the controller 12 initiates the output (Detergent Feed) andFLAG 3 is cleared 56. An output ON time (SET-TIME) is then calculated58.

Next, the intermediate flow-rate calculation is initiated 60. If thecontroller 12 determines that the flow-rate has increased to the pointwhere overshoot occurs, then the detergent feed is terminated 62. If theflow-rate has not increased, the accumulated ON time (Ta) is incremented64 and compared with the SET-TIME 66. If the accumulated ON time is notgreater than the SET-TIME, then the flow-rate calculation continues.However, if the accumulated ON time is greater than the SET-TIME, thedetergent feed is terminated 62. Whenever the detergent feed isterminated in the above steps 62, the OFF-TIME timer (To) is incremented68 and the controller 12 determines whether the flow-rate shouldcontinue to be calculated 70 by determining whether FLAG 2 has been set.If FLAG 2 has not been set, the flow-rate calculation continues 72.Otherwise, the remaining OFF-TIME is compared to the latency time asdiscussed below 90. When the flow-rate calculation is resumed 72, thedetergent concentration 28 is read every 0.1 seconds. The value of thedetergent concentration 28 is then stored in a memory location indicatedby a pointer A 72. The pointer A is then incremented to the next memorylocation so that the number of stored detergent concentration 28 valuescan be counted 74. Once thirteen detergent concentration 28 values havebeen stored (A>12), then an intermediate flow-rate (Fco) is calculated76. If Fco has not exceeded 35 microsiemens per second or FLAG 1 is notset 78, the flow-rate is deemed to have not changed and the latency time(LT) is incremented 80. The maximum latency time permitted is 20seconds. If the output is ON and some latency time has accumulated, butnot exceeding 20 seconds 82, then intermediate flow-rate calculation isrepeated (back to 60). If the flow-rate is deemed to have changed orifthe latency time is greater than 20 seconds, the flow-rate is set tothe latest flow-rate 84 and FLAG 1 is set to stop accumulating latencytime. With the output OFF, the latency time (LT) and flow-rate (FC)calculations continue if there are more than 2 seconds of OFF-TIME (To)remaining 86 and the OFF-TIME is not greater than the latency time 90.If there are not more than 2 seconds of OFF-TIME remaining 86, then FLAG2 is set 88. If the OFF-TIME is greater than the latency time 90, theflow-rate is cleared 92. The accumulated on-time, off-time, the storagedevice, FLAG 1, and FLAG 2 are also cleared 92. The latency time is thenreset to one 94. Finally, FLAG 3 is set 96 and recalculation beginsagain 52 by determining if the detergent feed will be on longer than twoseconds, given the last known flow-rate (FC), the current detergentconcentration (DC) and set-point (DS).

In summary, the present invention is a detergent controller having theability to change the detergent concentration set-point to correspond tomeal periods, as well as weekend and holiday workloads. The inventionincorporates a microprocessor, a clock and controller in one unit. Thus,in addition to detecting and recording warewashing machines performancedata, the unit can be programmed to control different set-points atdifferent time settings. The present invention also controls detergentlevels by balancing overshoot of the detergent set-point with the needto reach a suitable detergent concentration quickly. By optimizing thedetergent concentration level without incurring overshoot, thecontroller insures adequate washing performance on the first itemsthrough the process, and reduces chemical feeder wear.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations-are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

Those skilled in the art will recognize that the present invention couldbe used with different components or combinations of components thanthose described above. Those skilled in the art will also recognize thatother user interfaces and storage devices and different combinationsthereof, could be substituted for the interfaces and storage devicesused in the preferred embodiment.

What is claimed is:
 1. An apparatus for optimizing detergentconcentration in a warewashing machine with minimal overshoot,comprising:means for determining whether a detergent needs to be addedto a wash solution; means for feeding the detergent into the washsolution; sensor means for measuring a detergent concentration in thewash solution; means for calculating a rate of increase for thedetergent concentration in the wash solution; and means for determiningan appropriate on-time and off-time for the means for feeding usingderivative control, wherein the appropriate on-time and off-time isdetermined based on balancing the rate of increase for the detergentconcentration in the wash solution and compensation for any latency timewith a need to minimize overshoot in the detergent concentration whereinthe means for determining further comprises means for discontinuing themeans for feeding when overshoot in the detergent concentration isanticipated based upon the rate of increase.
 2. The apparatus of claim1, wherein the means for determining further comprises:means forincrementing an accumulated on-time measurement; means for calculatingan on-time; means for comparing the accumulated on-time with thecalculated on-time; and means for ending a detergent feed when theaccumulated on-time is greater than the calculated on-time.
 3. Theapparatus of claim 2, wherein the means for ending furthercomprises:means for advancing an off-time timer; means for resolvingwhether a flag indicating cessation of the detergent feed has been set;and means for continuing the means for feeding when the flag has notbeen set.
 4. The apparatus of claim 1, wherein the means for determiningfurther comprises:means for deciding whether a predetermined number ofdetergent concentration values have been stored in a memory device;means for computing an intermediate detergent flow-rate once thepredetermined number of detergent concentration values have been stored;means for ascertaining whether the intermediate detergent flow-rate haschanged; and means for setting the intermediate detergent flow-rate to alatest calculated detergent flow-rate when the intermediate detergentflow-rate has changed.
 5. The apparatus of claim 4, wherein the meansfor deciding further comprises:means for establishing a detergentconcentration once every predetermined interval; means for storing thedetergent concentration in a memory device; means for incrementing aregister of the memory device;and means for recalculating theintermediate detergent flow-rate when less than the predetermined numberof detergent concentration values have been stored.
 6. The apparatus ofclaim 4, wherein the means for ascertaining further comprises:means forincreasing a latency time when the intermediate detergent flow-rate hasnot changed; means for discovering whether an accumulated latency timeexceeds a predetermined period of time; means for recomputing theintermediate detergent flow-rate when the predetermined period of timehas not occurred; means for fixing the intermediate detergent flow-rateto the latest computed detergent flow-rate when the latency time exceedsthe predetermined period of time; and means for resetting theintermediate detergent flow-rate when the off-time is not greater thanthe latency time.
 7. The apparatus of claim 1, further comprising meansfor accounting for any latency time between activating a detergent feedand reading the detergent concentration information at a wash tanksensor.
 8. A method of optimizing detergent concentration in awarewashing machine using a controller, comprising the stepsof:determining, in the controller, whether a detergent needs to be addedto a wash solution in the warewashing machine; feeding the detergentinto the wash solution under a control of the controller; measuring, inthe controller, a detergent concentration in the wash solution using asensor coupled to the controller; calculating, in the controller, a rateof increase for the detergent concentration in the wash solution; anddetermining, in the controller, an appropriate on-time and off-time forthe feeding step, wherein the appropriate on-time and off-time isdetermined based on balancing the rate of increase for the detergentconcentration in the wash solution and compensation for any latency timewith a need to minimize overshoot in the detergent concentration,wherein the determining in the controller an appropriate on-time andoff-time step further comprises a step of discontinuing the feeding stepwhen overshoot in the detergent concentration is anticipated based uponthe rate of increase.
 9. The method of claim 8, wherein the determiningin a controller an appropriate on-time and off-time step furthercomprises the steps of:incrementing an accumulated on-time measurement;calculating an on-time; comparing the accumulated on-time with thecalculated on-time; and ending a detergent feed when the accumulatedon-time is greater than the calculated on-time.
 10. The method of claim9, wherein the ending step further comprises the steps of:advancing anoff-time timer; resolving whether a flag indicating cessation of thedetergent feed has been set; and continuing the feeding step when theflag has not been set.
 11. The method of claim 8, wherein thedetermining in a controller an appropriate on-time and off-time stepfurther comprises the steps of:deciding whether a predetermined numberof detergent concentration values have been stored in a memory device;computing an intermediate detergent flow-rate once the predeterminednumber of detergent concentration values have been stored; ascertainingwhether the intermediate detergent flow-rate has changed; and settingthe intermediate detergent flow-rate to a latest calculated detergentflow-rate when the intermediate detergent flow-rate has changed.
 12. Themethod of claim 11, wherein the deciding step further comprises thesteps of:establishing the detergent concentration once everypredetermined interval; storing the detergent concentration in thememory device; incrementing a register of the memory device; andrecalculating the intermediate detergent flow-rate when less than thepredetermined number of detergent concentration values have been stored.13. The method of claim 11, wherein the ascertaining step furthercomprises the steps of:increasing a latency time when the intermediatedetergent flow-rate has not changed; discovering whether an accumulatedlatency time exceeds a predetermined period of time; recomputing theintermediate detergent flow-rate when the predetermined period of timehas not occurred; fixing the intermediate detergent flow-rate to thelatest computed detergent flow-rate when the latency time exceeds thepredetermined period of time; and resetting the intermediate detergentflow-rate when the off-time is not greater than the latency time. 14.The method of claim 8, further comprising a step of accounting for anylatency time between activating a detergent feed and reading thedetergent concentration information at a wash tank sensor.